FIG. 1 illustrates a user interaction in a touch screen system 10 which includes a touch screen device 12 and an active stylus 14. The touch screen system 10 further includes a touch screen controller (TSC) 16 which functions in a number of modes including a capacitive sensing mode to detect a touch made to the touch screen device by a user through either, or both, a body part of the user or the active stylus 14 being manipulated by the user. The touch screen controller 16 is operable in another mode to engage in bi-directional data communications with the active stylus 14 through the touch screen device 12.
The hand of the user may grab the touch screen device 12 as generally indicated at reference 18. Still further, the hand of the user may rest on the surface of the touch screen device 12 while manipulating the active stylus 14 as generally indicated at reference 20. The user's hand/finger/thumb and the active stylus 14 are grounded through a common ground connection using the user's body (represented by the capacitance Cb). The touch screen controller 16, on the other hand, has its own grounding connection (represented by the capacitance Ctsc) which is different from the grounding of the body. This difference in grounding can cause signal attenuation problems when the touch screen controller 16 is operating in a transmit data communication mode to send a data communications signal to the active stylus 14. In this operating mode, the signal transmitted by the touch screen controller 16 through the touch screen device 12 will be picked up by both the active stylus 14 and the body of the user (through the surface touches referenced at 18 and/or 20). Because the user's body is also providing the ground reference for the active stylus 14, the actual signal which is received by the active stylus itself will be attenuated. Indeed, the attenuation may be so severe that it precludes accurate detection of the data communication information being transmitted to the active stylus 14.
There is accordingly a need in the art for a way to detect a user touch and control operation of the touch screen system to mitigate the adverse effects of such a touch when transmitting a data communication from the touch screen device to the active stylus.